Cryogenic refrigeration apparatus

Abstract

A system for providing a cold environment which has a number of cooling stages with variable displacement volumes into which input fluid from a compressor flows in an input channel to and from the displacement volumes and output fluid flows in an output channel to the compressor. Volume changers vary the volumes of the displacement volumes and input fluid flowing to a first set of displacement volumes is pre-cooled by regenerative heat exchange and counterflow heat exchange and input fluid flowing to the final displacement volume is pre-cooled primarily by counterflow heat exchange. The volume changer at at least one of the stages is thermally decoupled from the input and output channels.

What is claimed is: 
     
       1. A system for producing a cold environment comprising fluid compression means for supplying fluid under pressure; a plurality of successive operating stages having variable displacement volumes;   volume-changing means for varying the volumes of said displacement volumes;   input channel means for permitting flow of fluid to and from said successive displacement volumes;   first means for permitting input fluid to be introduced under pressure from said fluid compression means into said input channel means for flow therein to said successive displacement volumes;   second means for permitting fluid in said input channel means to flow to said fluid compression means;   third means for permitting fluid at reduced pressure to flow from the final one of said displacement volumes into an output channel means, said output channel means permitting flow of output fluid to said fluid compression means;   whereby input fluid flowing from said fluid compression means under pressure in said input channel means to said first set of displacement volumes is pre-cooled by regenerative heat exchange with a portion of the structure of said input channel and by counterflow heat exchange with fluid flowing in said output channel means, and input fluid flowing in said input channel means to said final one of said displacement volumes is pre-cooled primarily by counterflow heat exchange with fluid flowing in said output channel; and   means for thermally decoupling the volume changing means of at least one of said successive operating stages from said input and said output channel means.   
     
     
       2. A system in accordance with claim 1 wherein at least one of said successive operating stages is formed as four concentric means which comprise a cylindrical piston means and first, second, and third cylindrical tubular means concentrically mounted with respect to each other and to said cylindrical piston means, said piston means moving reciprocally with respect to said first cylindrical tubular means, said input channel means being formed between said first tubular means and said concentric second tubular means, and said output channel means being formed between said second tubular means and said third tubular means. 
     
     
       3. A system in accordance with claim 2 wherein each of said one or more stages includes a sliding seal means positioned between said piston means and said first cylindrical tubular means. 
     
     
       4. A system in accordance with claim 2 and further including means for producing a selected flow pattern in at least one of said input and output channel means. 
     
     
       5. A system in accordance with claim 4 wherein said flow pattern producing means comprises a plurality of elements positioned in at least one of said input and output flow channel means. 
     
     
       6. A system in accordance with claim 5 wherein said elements comprise a plurality of pin elements positioned in a staggered manner on the surface of at least one of said first and second tubular means. 
     
     
       7. A system in accordance with claim 1 and further including means for producing a selected flow pattern in at least one of said input and output channel means. 
     
     
       8. A system in accordance with claim 7 wherein said flow pattern producing means comprises a plurality of elements positioned in at least one of said input and output flow channel means. 
     
     
       9. A system in accordance with claim 8 wherein said elements are formed of a different material than that of said tubular means. 
     
     
       10. A system in accordance with claim 1 wherein at least one of said successive operating stages comprises a cylindrical piston means and a concentric cylindrical tubular means, said piston means moving in a reciprocal manner with respect to said cylindrical tubular means, and   said decoupling means comprises a separate heat exchanger means which includes the input channel means and output channel means at said at least one operating stage.   
     
     
       11. A system in accordance with claim 10 wherein said separate heat exchanger means is a stacked screen heat exchanger. 
     
     
       12. A system in accordance with claim 10 wherein at least one stage includes a sliding seal positioned between said piston means and said cylindrical tubular means. 
     
     
       13. A system in accordance with claims 1, 2, or 10 wherein each of said operating stages other than said final stage includes tubular piston means and said final stage includes a solid cylindrical piston means, said tubular piston means and solid piston means being connected to each other. 
     
     
       14. A system in accordance with claim 13 wherein the solid cylindrical piston means of said final stage comprises a plurality of solid cylindrical segments coupled to each other by flexible joints. 
     
     
       15. A system in accordance with claim 14 where in said solid cylindrical segments are made of a material having a relatively low thermal conductivity. 
     
     
       16. A system in accordance with claim 15 wherein said material is stainless steel. 
     
     
       17. A system in accordance with claim 14, wherein said final stage includes centering means associated with each of said solid cylindrical segments for positioning said segments substantially concentrically within the cylindrical tubular means. 
     
     
       18. A system in accordance with claims 1, 2, or 10 wherein the volume-changing means at the final one of said successive operating stages includes a piston means moving reciprocally within a cylindrical tubular means, said cylindrical tubular means being made of a material having a relatively high thermal conductivity. 
     
     
       19. A system in accordance with claim 18, wherein said material is low carbon steel. 
     
     
       20. A system in accordance with claims 1, 2, or 10 wherein said system includes first, second and third successive operating stages, each stage including volume-changing means, input channel means and output channel means, said second stage extending spatially from said first stage and said third stage extending spatially from said second stage. 
     
     
       21. A system in accordance with claims 1, 2, or 10 wherein said system includes first, second and third successive operating stages, each stage including volume-changing means, input channel means and output channel means, said third stage being invertedly positioned within said second stage and said second and third stages being invertedly positioned within said first stage. 
     
     
       22. A system in accordance with claims 1, 2, or 10 wherein said volume-changing means includes separate, independently operating piston means in each of said successive operating stages,the piston means at each stage being moved at the same cyclic frequency to provide variable displacement volumes, and the positions of each said piston means as a function of time being independently selectable for each piston means. 
     
     
       23. A system in accordance with claim 22 and further including sliding seal means positioned between said separate piston means. 
     
     
       24. A system in accordance with claims 1, 2, or 10 wherein said volume-changing means include integrally formed and commonly operated piston means in a selected number of said successive stages and separately formed, independently operated piston means in the remaining ones of said successive stages. 
     
     
       25. A system in accordance with claim 24, wherein integrally formed, commonly operated piston means are used at all stages other than the final stage of said system and a separately formed, independently operated piston means is used at the final stage of said system. 
     
     
       26. A system in accordance with claims 1, 2, or 10 wherein said third means includes a valve which can operate at a temperature substantially below room temperature. 
     
     
       27. A system in accordance with claim 26 and further including a first volume means positioned between said valve means and said output channel means. 
     
     
       28. A system in accordance with claim 27 and further including a load contacting heat exchanger means coupled to said first volume means for providing enhanced thermal contact with a thermal load; and   a second volume means coupled to said heat exchanger means and to said output channel means.   
     
     
       29. A system in accordance with claim 28 wherein said heat exchanger means includes means for providing a direct thermal contact with said thermal load. 
     
     
       30. A system in accordance with claim 29 wherein said heat exchanger means includes a matrix of elements having a high thermal conductivity. 
     
     
       31. A system in accordance with claim 30 wherein said elements are sintered metal elements. 
     
     
       32. A system in accordance with claim 31 wherein said sintered metal elements are copper spheres. 
     
     
       33. A system in accordance with claim 28 wherein said load contacting heat exchanger means includes a plurality of fin means connected thereto, said fin means transferring heat from a fluid external to said system into a fluid within said load contacting means. 
     
     
       34. A system in accordance with claims 1, 2, or 10 and further including valve means positioned between said output channel means and said fluid compression means. 
     
     
       35. A system in accordance with claim 34, wherein said valve means, said first means, and said second means are spool valve means. 
     
     
       36. A system in accordance with claims 1, 2, or 10 and further including load contacting means positioned at one of said successive operating stages other than the final stage thereof. 
     
     
       37. A system in accordance with claims 1, 2, or 10 wherein the final one of said successive operating stages includes a cylindrical piston means and first and second concentric tubular means, the diametral clearance between said piston means and said first concentric tubular means of said final operating stage is between 0.0005 inches and 0.003 inches. 
     
     
       38. A system in accordance with claims 1 or 2 and further including a housing positioned above the first stage of said plurality of operating stages, said housing being at room temperature and a portion of said input channel means being in heat exchange relationship with said housing.